Some versions of stylish-haskell do need the ghc-lib flag (#3868)

* Some versions of stylish-haskell do need the ghc-lib flag

* Set it in the stack config not the cabal config

Author: michaelpj

cabal.project

@@ -54,6 +54,10 @@ constraints:
   text -simdutf,
   ghc-check -ghc-check-use-package-abis,
   ghc-lib-parser-ex -auto,
+  -- This is only present in some versions, and it's on by default since 
+  -- 0.14.5.0, but there are some versions we allow that need this 
+  -- setting
+  stylish-haskell +ghc-lib,
   -- Centos 7 comes with an old gcc version that doesn't know about
   -- the flag '-fopen-simd', which blocked the release 2.2.0.0.
   -- We want to be able to benefit from the performance optimisations

stack-lts21.yaml

@@ -65,6 +65,8 @@ configure-options:
 flags:
   haskell-language-server:
     pedantic: true
+  stylish-haskell:
+    ghc-lib: true
   retrie:
     BuildExecutable: false